194 REPORT—1899. 
connected with the throwing up of a small island off the coast of North- 
West Borneo, near to Labuan. 
The first of these disturbed an electrometer at Batavia at 7h. 14m. 20s. 
P.M., a Iagnetometer being disturbed two minutes later. These disturb- 
ances indicate the arrival of the larger waves, which coming from Labuan 
had travelled about 1,660 kms. The velocity of propagatiun of these 
movements may be taken at about 2°7 kms. per second. With this 
assumption the conclusion is that this earthquake originated at about 
Th. 4m. 20s. p.m., the time to travel to Batavia having been 10 minutes. 
The effect of the second earthquake was to disturb a magnetometer in 
Batavia at 5h. 22m. 45s. A.m., which by similar reasoning leads to the 
conclusion that it originated at about 5h. 13m. a.m. At Sandakan, which 
is about 300 kms. from the origin, it was noted at 5h. 18m. a.m., the 
inference from which is that the time at the origin would be about 
5h. 16m. a.m. The mean between these two determinations gives as an 
approximation for the true time at the origin 5h. 14m. 30s. a.m. 
Apparent Velocity of Preliminary Tremors. 
September 20 | September 21 
pag aan Locality | Velocity in kms. | Velocity in kms. 
of Observation , | per sec. : per sec. 
Time | Time aS 
| In Arc On Chord Are | Chord || | Are Chord 
H. M. 8. || He at. 8. 
be! = Origin 7420); — | — | 5 14.30) — = 
9046 | £302 | Nicolaiew 7 23 30). %s8 2) |e be 2s Oe 1220 11:0 
10212; 9150 | Potsdum 1-26, 0 78a 770 5,30, 0.) LO 9°8 
| (about) 
10545 | 9378 | Catania 7°25) Bi) SBE 7-5 5 29 82 | 11°6 10:3 
| 10656) 9453 | Ischia . . | 7 21 54) 101 90 || 5 28 12 | 129 115 
/10711| 9489 | R.di Papa .|7 25 0| 86 76 5 32. &| 10:1 89 
/10730| 9490 | Rome. . | 7 2154) 101 9-0 5 29 42 | 11-7 10-4 
11211} 9815 Edinburgh . | 7 56 0| 3°6 a 6 730| 3-4 30 | 
/11433|} 9954 | Shide . » 17 24.47 )0 93 ol 5 28 51 | 13:2 11:5 
} 
In discussing the above table, the Edinburgh records may at once be 
excluded as referring to large waves rather than to preliminary tremors. 
Making this exception then, it will be observed that the velocities for 
September 21, are greater than those for September 20. Now as these 
two earthquakes, as recorded in Europe, indicate initial impulses of about 
the same intensity, it is extremely likely that they radiated from their 
origins with equal velocities, and therefore the differences seen in the 
tables in all probability are dependent upon errors in the times calculated 
for the origins of these shocks for which there is no sure method of cor- 
rection. On comparing these velocities with velocities determined over 
paths of similar lengths (see ‘ British Association Report,’ 1897, p. 174) it 
is noticed that one set of results lie about as much above average deter- 
minations, as the other does below the same. 
_A fair approximation to truth may therefore possibly be obtained by 
taking the average results recorded for the two shocks. In doing this, 
Catania, Ischia, Rocca di Papa and Rome, may be placed together as 
representing a path, which for each is practically 96° in length. The 
result of this operation is as follows :— 
